1. Field of the Invention
This invention relates to an easily activable catalyst for, hydrotreatment of a hydrocarbon oil and to a method for the production thereof.
2. Description of the Prior Art
In the so-called hydrotreatment which consists in effecting hydrogenation, hydro-desulfurization, hydrodenitrification, hydrogenolysis, etc. of a hydrocarbon oil in the presence of hydrogen, the catalyst which has at least one metal from among the metals of Group 6 and the metals of Group 8 in the Periodic Table of Elements supported as an active ingredient for hydrotrentment on a carrier of such an inorganic oxide as alumina, silica-alumina, or titania is used. Mo and W are preferred choices among the metals of Group 6 and Co and Ni among these of Group 8.
The metal for this purpose is generally supported in the form of an oxide. Since the metal in this form possesses no activity, it must be subjected to presulfiding, i.e. activation by the conversion of the oxide form into the sulfide form, before it is put to use in the hydrotreatment.
It has been customary to effect the presulfiding by charging the catalyst in a reactor to be used for the hydrotreatment of a hydrocarbon oil and then passing a sulfiding agent in combination with hydrogen through the bed of catalyst. The operating conditions for the presulfiding are widely varied by the process of the hydrotreatment to be employed or by the kind of the sulfiding agent to be used. Where hydrogen sulfide is used as a sulfiding agent, for example, the presulfiding is effected by diluting this sulfiding agent with hydrogen to a concentration roughly in the range of 0.5 to 5% by volume and passing the resultant mixture in a total volume of 1,000 to 3,000 liters as computed under standard temperature and pressure per liter of the catalyst at a temperature not lower than 180.degree. C. (generally not lower than 250.degree. C.). Where carbon disulfide, normal butyl mercaptan, dimethyl sulfide, dimethyl disulfide, or the like is used as a sulfiding agent, it is put to use as diluted with a more volatile hydrocarbon oil, with the temperature in the range of 250.degree. to 350.degree. C., the pressure in the range of 20 to 100 kg/cm.sup.2, the space velocity of the liquid mixture in the range of 0.5 to 2 hr.sup.-1, and the hydrogen/oil ratio in the range of 200 to 1,000 N-liters/liter.
After this presulfiding operation is completed, the material being fed to the reactor is switched from the diluted sulfiding agent to the hydrocarbon oil as an actual raw material for treatment, to initiate the operation of the hydrotreatment.
Incidentally, since this operation of presulfiding predetermines the success or failure of the subsequent hydrotreatment, proper selection of raw materials to be used and deliberate execution of the procedure to be adopted are indispensable requirements. In the use of a diluent, for example, if the diluent happens to contain an olefin, the presulfiding possibly polymerizes the olefin and the produced polymer poisons the catalyst. The hydrocarbon oil to be used as a diluent, therefore, must be of a type not containing any olefin. A less volatile hydrocarbon oil is not suitable as a diluent because it possesses too high viscosity to manifest a desired effect in wetting the surface of the catalyst. Thus, there is no alternative but to use a more volatile oil. The use of such a more volatile oil entails an increase in cost. The catalytic metal has the possibility of being inactivated when it is suffered to react with hydrogen at elevated temperatures and consequently undergo reduction. To preclude this inactivation, the sulfiding agent must be used rather generously. The proportions of the sulfiding agent and hydrogen must be properly maintained. Generally, the presulfiding of the nature described above is carried out over a period of several days. Since this operation by nature is performed temporarily, it is not automated in most cases. Since the operation inevitably involves extraordinary complicated steps, the operator is compelled to endure a heavy burden. In the circumstances, the obviation of the necessity for this presulfiding or at least the alleviation of the complicacy of the operation has constituted itself a task.
Recently, a method which can fulfil this task has been proposed.
This method comprises impregnating a catalyst formed of a deposited active metal with a polysulfide represented by the general formula, R--S(n)--R' (wherein n stands for an integer in the range of 3 to 20 and R and R' independently stand for a hydrogen atom or an organic group having 1 to 150 carbon atoms per molecule) and heat-treating the impregnated catalyst in the absence of hydrogen gas at a temperature in the range of 65.degree. to 275.degree. C. under a pressure in the range of 0.5 to 70 bars (Japanese Patent Application Disclosure SHO No. 61(1986)-111,144). In accordance with this method, since the polysulfide which has impregnated the catalyst is caused by the subsequent heat treatment to sulfide the active metal, the presulfiding to be performed in the reactor has no use for the sulfiding agent or the diluent and, therefore, can be effected with an easy operation. The presulfiding, when desired, may be performed outside the reactor. In this case, the catalyst which has undergone the presulfiding is ready to be packed in the reactor and put to use immediately in initiating the hydrotreatment.
The amount of the aforementioned polysulfide to be used is a stoichiometric amount necessary for subsequent thorough sulfiding of the whole active metal oxide (such as, for example, NiO or MoO.sub.3) present in the catalyst. This polysulfide is diluted with a suitable organic solvent and, as such, caused to impregnate the catalyst. In impregnating a catalyst which has a large loaded active metal content, therefore, the aofrementioned polysulfide solution to be used must be in a high concentration. Since the polysulfide mentioned above has a high visosity, the possibility ensures that the compound, when used in the form of a solution of high concentration, penetrates small pores of the catalyst with difficulty.